Method for fabricating a protective cap for an optical waveguide core of a planar lightwave circuit device

Abstract

In a planar lightwave circuit, a method of making an optical waveguide that resists core deformation. The method includes a step of forming a core layer on a bottom clad. A waveguide core is formed from the core layer using an etching process. The waveguide core is fabricated to have a higher refractive index than the bottom clad. A silica glass cap layer is then formed over the waveguide core and the bottom clad. A top clad is then formed over the waveguide core, the silica glass cap layer, and the bottom clad. The waveguide core has a higher refractive index than the top clad. The silica glass cap layer maintains the shape of the waveguide core during an anneal process of the top clad. The silica glass cap layer can be deposited using PECVD (plasma enhanced chemical vapor deposition). The silica glass cap layer can be between 0.3 to 2 microns thick. The silica glass cap layer can be undoped silica glass. The silica glass cap layer can have a higher reflow temperature than the waveguide core to prevent deformation of the waveguide core. The silica glass cap layer also can prevent diffusion of dopant between the waveguide core and the top clad.

What is claimed is:  
     
         1 . In a planar lightwave circuit, a method of making an optical waveguide that resists core deformation, comprising the steps of: 
 a) forming a core layer on a bottom clad;    b) forming a waveguide core from the core layer using an etching process, the waveguide core having a higher refractive index than the bottom clad;    c) forming a silica glass cap layer over the waveguide core and the bottom clad;    d) forming a top clad over the waveguide core, the silica glass cap layer, and the bottom clad, the waveguide core having a higher refractive index than the top clad, wherein the silica glass cap layer maintains the shape of the waveguide core during an anneal process of the top clad.    
     
     
         2 . The method of  claim 1  further including the step of using an etching process to remove that portion of the silica glass cap layer deposited on the bottom clad during step c) by using an etching process.  
     
     
         3 . The method of  claim 1  wherein the silica glass cap layer is between 0.3 to 2 microns thick.  
     
     
         4 . The method of  claim 1  wherein the silica glass cap layer is undoped silica glass.  
     
     
         5 . The method of  claim 1  wherein the silica glass cap layer is configured to prevent diffusion of dopant between the waveguide core and the top clad.  
     
     
         6 . The method of  claim 1  wherein the silica glass cap layer is deposited using PECVD (plasma enhanced chemical vapor deposition).  
     
     
         7 . The method of  claim 1  wherein the silica glass cap layer has a higher reflow temperature than the waveguide core.  
     
     
         8 . A method of making a capped optical waveguide core for a planar lightwave circuit, the method comprising the steps of: 
 a) forming a bottom clad on a silicon substrate;    b) forming a core layer on the bottom clad, the core layer having a higher refractive index than the bottom clad;    c) forming a core from the core layer; and    d) forming a silica glass cap layer over the core and the bottom clad;    e) forming a top clad over the core wherein the cap layer prevents core deformation during an anneal process of the top clad, wherein the anneal process is at a temperature of at least 1000 C.    
     
     
         9 . The method of  claim 8  further including the step of using an etching process to remove that portion of the silica glass cap layer deposited on the bottom clad during step c) by using an etching process.  
     
     
         10 . The method of  claim 8  wherein the silica glass cap layer is between 0.3 to 2 microns thick.  
     
     
         11 . The method of  claim 8  wherein the silica glass cap layer is undoped silica glass.  
     
     
         12 . The method of  claim 8  wherein the silica glass cap layer is configured to prevent diffusion of dopant between the waveguide core and the top clad.  
     
     
         13 . The method of  claim 8  wherein the silica glass cap layer is deposited using PECVD (plasma enhanced chemical vapor deposition).  
     
     
         14 . The method of  claim 8  wherein the silica glass cap layer has a higher reflow temperature than the waveguide core.  
     
     
         15 . A method of making a silica glass cap for protecting the shape of the waveguide core during an anneal process for the top clad, comprising the steps of: 
 a) forming a silica glass cap layer over the waveguide core, wherein the silica glass cap layer is between 0.3 to 2 microns thick; and    b) forming a top clad over the waveguide core, the silica glass cap layer using a multistep deposition and anneal process, wherein the silica glass cap layer maintains the shape of the waveguide core during the anneal process.    
     
     
         16 . The method of  claim 15  wherein the silica glass cap layer is undoped silica glass.  
     
     
         17 . The method of  claim 15  wherein the silica glass cap layer is deposited using PECVD (plasma enhanced chemical vapor deposition).  
     
     
         18 . The method of  claim 15  wherein each of the steps of the anneal process from step c) are at a temperature of at least 1000 C.